Heavily enriched: An energy-efficient way of enriching hydrogen isotopes
in silicon

Date:
August 16, 2021
Source:
Nagoya City University
Summary:
Deuterium, a heavier but less abundant version of the hydrogen atom,
has many practical applications. Unfortunately, producing deuterium
and using it to protect silicon-based semiconductors requires a
lot of energy and very expensive deuterium gas. Now, scientists
have discovered an energy- efficient exchange reaction to swap
hydrogen atoms for deuterium on the surface of nanocrystalline
silicon. Their results pave the way to more durable electronic
devices while keeping costs and the environmental impact low.



FULL STORY ==========================================================================
The discovery of isotopes in the early 20th century marked a key moment
in the history of physics and led to a much more refined understanding
of the atomic nucleus. Isotopes are 'versions' of a given element of
the periodic table that bear the same number of protons but a different
number of neutrons, and therefore vary in mass. These differences in
mass can radically alter certain physical properties of the atoms, such
as their radioactive decay rates, their possible reaction pathways in
nuclear fission reactors, and much more.


========================================================================== While most isotopes of an element share similar chemical properties,
there is one notable exception: hydrogen isotopes. Most hydrogen atoms
on Earth contain only one proton and one electron, but there exist
hydrogen isotopes which also have one neutron (deuterium) or two neutrons (tritium). Deuterium, which essentially weighs twice as much as 'normal' hydrogen, has found many practical and scientific uses. For example, it
can be used to label and track molecules such as proteins to investigate biochemical processes. It can also be strategically used in drugs to
reduce their metabolic rate and increase their half-life in the body.

Another important application of deuterium exists in the field of
semiconductor electronics. The surface of silicon-based semiconductors
has to be 'passivated' with hydrogen to ensure silicon atoms don't come
off (desorb) easily, thereby increasing the durability of microchips, batteries, and solar cells. However, through mechanisms that are still not completely understood, passivation with deuterium instead of hydrogen
results in desorption probabilities about one hundred times lower,
implying that deuterium may soon become an indispensable ingredient in electronic devices. Unfortunately, both the procurement of deuterium and available techniques to enrich silicon surfaces with it are very energy inefficient or require very expensive deuterium gas.

Fortunately, at Nagoya City University (NCU), Japan, a team of scientists
led by Professor Takahiro Matsumoto have found an energy-efficient
strategy to enrich silicon surfaces using a dilute deuterium
solution. This study, which was published in Physical Review Materials,
was carried out in collaboration with Dr. Takashi Ohhara of Japan Atomic
Energy Agency and Dr. Yoshihiko Kanemitsu from Kyoto University.

The researchers found that a peculiar exchange reaction from hydrogen to deuterium can occur on the surface of nanocrystalline silicon (n-Si). They demonstrated this reaction in thin n-Si films submerged in a deuterium- containing solution using inelastic neutron scattering. This spectroscopy technique involves irradiating neutrons onto a sample and analyzing
the resulting atomic motions or crystal vibrations. These experiments,
coupled with other spectroscopy methods and energy calculations based
on quantum mechanics, revealed the underlying mechanisms that favor
the replacement of hydrogen terminations on the surface of n-Si with
deuterium: The exchange process is closely related to differences in
the surface vibrational modes between hydrogen- and deuterium-terminated
n-Si. "We achieved a fourfold increase in the concentration of surface deuterium atoms on n-Si in our experiments performed in the liquid
phase," highlights Dr. Matsumoto, "We also proposed a gas-phase enrichment protocol for n-Si that, according to our theoretical calculations, could enhance the rate of deuterium enrichment 15-fold." This innovative
strategy of exploiting quantum effects on the surface of n-Si could
pave the way to new methods to procure and utilize deuterium. "The
efficient hydrogen-to-deuterium exchange reaction we reported may lead
to sustainable, economically feasible, and environment-friendly deuterium enrichment protocols, leading to more durable semiconductor technology," concludes Dr. Matsumoto.

The NCU team also stated that "It has been theoretically predicted that
the heavier the hydrogen is, the higher the efficiency of the exchange
reaction is.

Thus, we can expect more efficient enrichment of tritium atoms on
n-Si, which leads to the possibility of purifying tritium contaminated
water. We believe that this is an issue that must be urgently solved."
Let us hope the findings of this work allow us to benefit more from the
heavier isotopes of hydrogen without taking a toll on our planet.

========================================================================== Story Source: Materials provided by Nagoya_City_University. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Takahiro Matsumoto, Ikumi Nomata, Takashi Ohhara, Yoshihiko
Kanemitsu.

Determination of localized surface phonons in nanocrystalline
silicon by inelastic neutron scattering spectroscopy and its
application to deuterium isotope enrichment. Physical Review
Materials, 2021; 5 (6) DOI: 10.1103/PhysRevMaterials.5.066003 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/08/210816125725.htm

--- up 14 weeks, 3 days, 22 hours, 45 minutes
* Origin: -=> Castle Rock BBS <=- Now Husky HPT Powered! (1:317/3)